The invention is a hydrostatically driven working device, in particular a core sampler and a CPT sampler for investigation of sediments on the bottom of the sea, said working device comprising an outer tube (cylinder tube) and an inner tube (sampling tube), or a probe (CPT probe), having a piston fastened to the upper end of the tube/probe and a lead-through having a seal which surrounds the tube/probe at the lower end. This lead-through contains a valve for injecting and discharging air from the space between the outer and inner tube/probe, confined between the piston and the lower lead-through.
To the upper end of the outer tube is fastened a lead-through similar to the lower lead-through, without any air valve, said lead-through having no throughgoing bore for CPT, and to this lead-through is fastened an ear for attachment of a raising wire and with the possibility of attaching a wire for the piston. To the lower lead-through may be fastened a suction anchor for retaining to the bottom during the working stroke.
The working stroke starts when the raising wire becomes so slackened that the spring may open the valve which admits water through the choke valve to the piston, which is driven slowly downwardly, until the neck of the piston, having the same diameter as the sampling tube, passes the seals, and the working stroke starts when the water gets free access to the area between the outer and inner tube, the space between the piston and the lower lead-through being filled by air at an excess pressure which keeps the piston in its upper position until the valve opens.
For CPT the entire area above the piston will be a pressure area, and the stroke velocity will be adjusted to 2 cm/sec. by a pressure compensated flow rate regulation valve. Upon termination of the stroke the air cushion between the piston and the lower lead-through will expand and pull the tube back to its origin during pull-up. The liner will be confined between the catcher at the lower end and the clamping sleeve at the upper end. For expelling of the liner with the sample the clamping sleeve is removed and a piston is inserted in the neck of the piston, and a cover having supply of water is screwed into the neck, whereupon water having an excess pressure pushes out the liner and the sample.
By use of the same technique as for driving the sampling tubes into the sediment support legs may be shot down into the sediment in order to stabilize the sampler, said support legs being fastened to a device which can slide along the outer tube, the plate connecting the support legs being a brake against the raising forces during the shoot-down.
The invention may be combined as a twin, with one unit being a corer and another being CPT (Core Penetration Test), firmly connected to each other.